This invention relates to catalytic hydrotreatment of petroleum distillates and similar hydrocarbon materials. More particularly, this invention relates to the use of catalyst comprising a chromium component with molybdenum and Group VIII metal components, in such hydrotreating processes.
In the petroleum refining industry, hydrotreating processes are in wide use for effecting hydrodesulfurization and other upgrading treatment of hydrocarbon stocks, typically carried out in the presence of a catalyst. Hydrofining refers generally to the treatment of solvents and distillates with hydrogen and is typically a catalytic hydrogenation. Hydrofining is employed to remove sulfur, nitrogen and other nonhydrocarbon components, as well as to improve the odor, color, stability, and other important quality characteristics. Typical applications range from relatively mild hydrosweetening operations carried out at high space velocities, very low pressures and temperatures, and minimal hydrogen consumption, to more severe operations such as desulfurization and denitrification of heavy vacuum gas oils, decanted oils and lubricating oils. Sulfur and nitrogen compounds are often poisonous to the activity of catalysts employed when such carbonaceous feedstocks are further processed such as in hydrocracking and fluid catalytic cracking. When applied for processing catalytic cracking feedstocks, hydrofining can significantly reduce catalyst coking and improve the quality of catalytic cracking stock resulting in increased gasoline yield as well as sulfur or nitrogen removal.
Generally, the catalysts employed in hydrofining are comprised of composites of Group VIB or Group VIII metal hydrogenating components, or both, with an inorganic oxide base, or support, typically alumina. For example U.S. Pat. No. 3,245,919, Gring, et al., discloses hydrocarbon conversion processes that employ a catalyst containing a catalytic amount of a metal component selected from metals of Group VI and Group VIII supported on alumina. The patent summarizes the prior art catalyst materials which can include compounds of Groups VI and VIII metals such as chromium, molybdenum, tungsten, iron, nickel cobalt, and the platinum group noble metals, or mixtures of two or more such compounds (column 6, lines 12 through 19), but does not disclose an example of chromium and molybdenum in the same catalytic composition. Gring specifically discloses catalytic compositions in which only one of the two Group VI metals is employed and teaches the use of the catalytic composition containing molybdenum with cobalt for desulfurization and the catalyst containing chromium for dehydrogenation.
U.S. Pat. No. 3,114,701, Jacobson, et al., refers in general to prior art processes for hydrofining hydrocarbon oil by contact with various catalysts, generally comprising chromium and/or molybdenum oxides together with iron, cobalt, and/or nickel oxides on a porous oxide support, such as alumina or silica-alumina (column 1, lines 25 through 30). However, this patent teaches a hydrodenitrification process employing a catalyst containing large concentrations of nickel and molybdenum on a predominantly alumina carrier; the patent does not provide any examples using a specific catalytic composition comprising chromium, molybdenum, and a Group VIII metal.
U.S. Pat. No. 2,577,823 (Stine, 1951) discloses that heavy hydrocarbon fractions, such as gas oil and reduced crude, can be hydrodesulfurized over a catalyst consisting of chromium, molybdenum, and aluminum oxides, but this patent does not disclose or suggest that a Group VIII metal component be incorporated in such catalyst.
U.S. Pat. No. 3,265,615 (Buss, 1966) discloses a method for hydrotreating hydrocarbon oil employing a catalyst comprising chromic sulfide and molybdenum sulfide prepared by the particular method of his invention. Buss discloses that in contrast to prior art catalysts containing both a Group VI and a Group VIII component, the "absence of a Group VIII component" in the catalyst prepared by his method permits an advantage in the removal of nitrogen, as pointed out in column 5, lines 35-50. Buss discloses a catalyst prepared by impregnating an alumina support with ammonium molybdate, then drying and calcining to produce a molybdenum oxide-alumina precursor which was then impregnated with an aqueous solution of chromic sulfate and dried overnight at low temperature; Buss teaches that the chromic sulfate must be subsequently reduced by treatment with hydrogen, and then the material is sulfided to produce the chromium sulfide-molybdenum sulfide-alumina catalyst. In contrast, the catalyst employed in the process of the present invention comprises a Group VIII metal component and the catalyst does not require reduction of sulfate to sulfide in its preparation.
French Patent Publication No. 2,281,972 discloses the preparation of a catalyst comprising the oxides of cobalt, molybdenum, and/or nickel on a base of both alumina oxide and 3 to 15 wt.% chromium oxide and its use for the refining of hydrocarbon fractions such as the hydrodesulfurization of fuel oils obtained by vacuum distillation or residual oils obtained by atmospheric distillation. The support base of this catalyst is composed of aluminum oxide and chromium oxide and is preferably prepared by the coprecipitation of compounds of chromium and aluminum; in contrast the catalyst employed in the process of the present invention comprises an inorganic oxide support, preferably alumina, upon which a compound of chromium is deposed or impregnated.
Quick et al. in copending U.S. patent application Ser. No. 967,413, (now U.S. Pat. No. 4,181,602) filed Dec. 7, 1978, which is incorporated herein by reference, discloses a process for hydrotreating a heavy hydrocarbon stream containing metals, asphaltenes, nitrogen compounds, and sulfur compounds, which process comprises contacting said stream under suitable conditions and in the presence of hydrogen with a catalyst comprising a hydrogenating component selected from the group consisting of (1) molybdenum, chromium and a small amount of cobalt, (2) their oxides, (3) their sulfides, and (4) mixtures thereof on a large-pore, catalytically active alumina. Quick et al. disclose that such process is particularly useful for hydrotreating heavy hydrocarbon streams such as petroleum residua, both atmospheric resids and vacuum resids, tar sands oils, tar sands resids, and liquids obtained from coal. This application also suggest that such process can be employed to satisfactorily hydrotreat petroleum hydrocarbon distillates, such as gas oils, cycle stocks, and furnace oils; however, no example of the treatment of such distillate is presented.
Typical commercial hydrofining catalysts are molybdena on alumina, cobalt molybdate on alumina, nickel molybdate on alumina or nickel tungstate on alumina. The specific catalyst used depends on the particular application. Cobalt molbydate catalyst is often used when sulfur removal is the primary interest. The nickel catalysts find application in the treating of cracked stocks for olefin or aromatic saturation. Sweetening to remove mercaptans is a preferred application for molybdena catalysts. Denitrification is generally effected by the use of a supported sulfided catalyst containing nickel and molybdenum.
The primary objective of the present invention is to achieve improved hydrotreating of petroleum distillates and similar materials. An additional objective is to provide improved catalyst for use in such hydrotreating processes.
We have found that the objects of this invention can be achieved by contacting hydrocarbon streams such as petroleum distillates and similar materials with hydrogen and a catalyst comprising chromium, molybdenum, and at least one Group VIII metal hydrogenation components deposited on a porous refractory inorganic oxide support of a specified pore size, which is effective in the removal of both sulfur and nitrogen from such hydrocarbon streams, in contrast to catalyst which does not contain chromium with Group VIII metal. While catalysts comprising chromium, molybdenum, and at least one Group VIII metal hydrogenation component deposited on a porous refractory inorganic oxide support are effective in the removal of both sulfur and nitrogen from hydrocarbon streams, the catalysts of this invention having a pore volume distribution comprising 20-50% of pore volume in pores with diameters of 0-50 Angstrom units, 30-70% of pore volume in pores with diameters of 50-100 Angstrom units, 0-20% of pore volume in pores with diameters of 100-150 Angstrom units, and 0-10% of pore volume in pores with diameters greater than 150 Angstrom units are unexpectedly superior to the various other catalysts based on chromium, molybdenum, and Group VIII metal for treating petroleum distillates and the like. In particular, catalysts having the aforesaid pore distribution lose substantially no activity in sulfur and nitrogen removal after 20 days on oil whereas similar catalysts having the pore distribution of the aforesaid Quick et al. U.S. application Ser. No. 967,413 have reduced nitrogen removal properties in approximately 12-16 days on oil. Other things being equal, the chromium catalysts of this invention are so stable that they permit the use of reactors of markedly smaller size than prior art reactors (up to 1/5 the size for gas oil treatment with nonchromium catalysts and up to 1/2 the size for gas oil treatment with the chromium catalysts of the Quick et al. application).
Typical feedstocks that can be treated satisfactorily by the process of the present invention generally comprise distillates from petroleum and tar sands as well as similar materials such as shale oil and fractions thereof. Generally, these hydrocarbon streams are substantially free from asphaltenic materials and will usually contain only trace amounts of metals such as nickel and vanadium, thus permitting sulfur and nitrogen to be removed more readily than such removal from heavy hydrocarbon streams such as petroleum resid and whole tar sands oil. While lighter distillates such as naphthas, kerosene and diesel fractions can be treated by the process of the present invention, particularly effective removal of sulfur and nitrogen from heavier distillate such as gas oils, decanted oils, lubricating oils and recycle streams can be obtained employing the process of this invention in more severe operation. Typical heavy gas oil streams are obtained by vacuum distillation of petroleum as well as gas oils obtained by coking reduced crude, vacuum resid and similar materials such as tar sands oil. In addition to removing sulfur and nitrogen, treatment of gas oil and similar heavy distillate streams at high temperature in the process of this invention can achieve substantial hydrocracking of heavy components in such feedstocks.
The hydrogenation components of the catalyst employed in the process of the present invention comprise chromium, molybdenum, and at least one Group VIII metal, preferably cobalt; as used herein, the term "hydrogenation components" is meant to include Group VIII metal, molybdenum, and chromium present in the catalyst in the elemental form, as oxides of the metals, as sulfides of the metals, or mixtures thereof. Group VIII metals selected from iron, cobalt, nickel, ruthenium, rhodium, platinum, palladium, osmium, and iridium, can be employed as a hydrogenation component and cobalt is the preferred Group VIII metal component. Suitably, the Group VIII metal, exemplified by cobalt, is present in the catalyst in the range of about 0.1 wt.% to about 5 wt.%, calculated as the oxide of the metal and based upon the total catalyst weight; the chromium is present in an amount within the range of about 5 wt.% to about 30 wt.%, calculated as Cr.sub.2 O.sub.3 and based upon the total catalyst weight, and molybdenum is present in an amount within the range of about 5 wt.% to about 20 wt.%, calculated as MoO.sub.3 and based upon the total catalyst weight. Preferably, the cobalt is present in an amount within the range of about 0.5 wt.% to about 2.5 wt.%, calculated as CoO and based upon the total catalyst weight, the chromium is present in an amount within the range of about 7-20 wt.%, calculated as Cr.sub.2 O.sub.3 and based upon the total catalyst weight, and the molybdenum is present in an amount within the range of about 7-15 wt.%, calculated as MoO.sub.3 and based upon the total catalyst weight, such components being deposited on a catalytically active alumina support. Chromium and molybdenum contents of the catalyst in excess of these preferred ranges add expense and appear to provide no appreciable gain in catalyst activity, while levels of chromium and molybdenum less than these preferred ranges appear to provide decreased catalyst activity; a cobalt content in excess of the preferred range appears to cause accelerated deactivation of the catalyst, yet the cobalt content should not be less than the preferred range in order to provide sufficient activity for commercial use.